In the art of filter making, it is highly desirable to provide high efficiency and often low pressure drop filter. This is particularly an advantage in connection with cigarette filters. Many filtering procedures have been employed in an attempt to direct and control the flow of smoke from the tobacco through the filter to the smoker wherein the filtering process is highly efficient without significatnly increasing the pressure differential across the filter.
Naturally, the filter rod assembly for use in meeting the above discussed criteria should be of simplified manufacture with as few component parts as possible. In this manner, a filter of the lowest possible cost and ease of handling and use can be employed. In fact, it would be extremely desirable to have a single piece of material which provides both the internal filtering structure and the external support structure.
Filters of the type of primary concern in the application are collectively known in the art as "pass" type filters. The majority of these filters generally depend upon inserting one preformed tube into another tube and providing a tortuous flow path for smoke therethrough. As stated above, it must be kept in mind that the tortuous flow path must be sufficient to provide high efficiency type filtering while generally reducing the pressure drop in connection with the smoke flow on both sides of the filter.